What's wrong with my tomatoes?

[Common_Clay]

Hi,

  I wondered if anyone could lend a hand with identifying a problem with my tomatoes... I'm growing a range of different varieties, all are in a mini greenhouse type of structure, so it's unheated but can become quite humid. The lower leaves have turned very dark, especially around the edges and nearly all the leaves on each plant near the top are speckled white/very light green. If I didn't know better, they'd almost look like a variegated leafed variety! I suspect this could be a common problem seeing as all my varieties are affected, but if not I'll add some photos.
  Hope someone can help. Thanks!

[Common_Clay]

[Jeannine]

Is it dusty, if you rub it with your finger does it rub off.

[Marymary]

Maybe it's scortching from the sun - quite a few of mine have got it too but seem to be growing well.

[Tin Shed]

Sounds like a mixture of being very cold, then as Marymary says, sunscorch. The weather has been all over the place, hot one day then very cold the next.